It is well known in the valve art that substantially greater power is required to operate valves that provide a zero leakage seal against flow pressure from two directions than is required to seal against flow pressure from one direction. Additionally, power requirements for such valves ascend in proportion to increases in system operating pressures that the valves must seal. For example, a common gate valve may provide a zero leakage seal against two-directional flow, wherein the gate valve includes a valve body that defines a central passage having a reduced diameter sealing shoulder around a circumference of the passage through which the fluid flows, and an adjustable gate having a sealing surface that is positioned so that a peripheral edge of the sealing surface contacts the sealing shoulder to seal the central passage of the valve body against any fluid flow. The sealing surface is adjustably moved away from the sealing shoulder to permit fluid flow. Moving the gate into and out of contact with the sealing shoulder requires application of adequate power to overcome two primary forces; namely--friction between the sealing surface and sealing shoulder, and pressure on the gate from the fluids contained within the central passage.
Efforts to reduce required power to operate such valves have resulted in many differing valve structures including a two-stage gate valve, wherein the sealing surface in a first stage is displaced away from the sealing shoulder in a direction that is parallel to the flow of the fluid in the passage. Next, in a second stage, the sealing surface is moved out of the passage. By moving the sealing surface parallel to the flow of fluids in the first stage, friction between the peripheral edge of the sealing surface and the sealing shoulder is eliminated as the sealing surface moves in the second stage, and a flow gap is opened between the sealing surface and the sealing shoulder so that any pressure differential between upstream and downstream sides of the sealing surface is reduced. Elimination of the friction and reduction of the pressure differential reduces power requirements to move the gate out of the passage. The reduction of power is significant when the movement of the sealing surface in the first stage is both parallel to and also in the direction of the fluid flow. However, in a two-directional flow system, the required power will eventually have to be adequate to move the sealing surface in a direction opposite to the direction of fluid flow, thereby requiring substantial power.
In working environments such as outer space, fluid control systems often include very high operating pressures, yet design parameters mandate valves having modest weight, power and volume components. Typically such valves are actuated by solenoids in response to control signals, and are often used to regulate pressurization of such facilities as laboratory research modules carried on board the United States "Space Shuttle". For example, a research module capable of sustaining human research activity for many hours pressurized to one (1) atmosphere would benefit by a valve capable of voiding test chambers within the module to the hard vacuum of outer space, wherein the valve has a conductance value of thirty (30) liters per second in a one and five-tenths (1.5) inch line-sized valve and the valve could be opened or closed at any time, while exposed to a pressure differential of 40 p.s.i.d. in either direction, through application of no more than thirty (30) watts of electrical power. Known reduced power valves are incapable of achieving such performance characteristics.
Accordingly, it is the general object of the present invention to provide a valve that overcomes the excessive power, weight and volume problems of the prior art.
It is a more specific object to provide a valve that minimizes power requirements in providing a zero leakage seal against flow pressure from two directions.
It is another specific object to provide a valve that compensates for non-linear force characteristics of common solenoids used to activate such a valve.
The above and other advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.